CMOS Doherty Ampli fier With V ariable Balun Transformer and Adaptive Bias Control for Wireless LAN Application Namsik Ryu, Seunghyun Jang, Kwang Chun Lee, and Y

Abstract

This paper presents a novel CMOS Doherty power amplifier (PA) with an impedance inverter using a variable balun transformer (VBT) and adaptive bias control of an auxiliary amplifier. Unlike a conventional quarter-wavelength trans- mission line impedance inverter of a Doherty PA, the proposed VBT impedance inverter can ach ieve load modulation without any phase delay circuit. As a result, a phase compensation circuit at the input path of the auxiliary ampli fier can be removed, and the total size of the Doherty PA can be reduced. Additionally, an enhancement of the power ef ficiency at backed-off power levels can successfully be achie v e dw i t ha na d a p t i v eg a t eb i a si na common gate stage of the auxiliary ampli fier. The PA, fabricated with 0.13-µm CMOS technology, achieved a 1-dB compression point (P1 dB) of 31.9 dBm and a power-added ef ficiency (PAE) at P1 dB of 51%. When the PA is tested with 802.11g WLAN orthogonal frequency division multiplexing (OFDM) signal of 54 Mb/s, a 25-dB error vector magn itude (EVM) compliant output power of 22.8 dBm and a PAE of 30.1% are obtained, respectively.